Start Niagara like it has run for a while

I am getting started with Niagara (and with particles in UE4 at all).
In my game I need some columns of thick smoke like the burning oil wells after the war in Iraq.
What I have achieved so far looks okay. But the emitters start just when the level is loaded. That means, that the columns of smoke have to build first.

So I wonder, if there is a way to get the emitters started, as if they have run for a while. So that the columns of smoke are already there, when the map starts.

Any help would be appreciated.